1. Field of the Invention
The present invention relates to an inkjet printing method and inkjet printing apparatus for printing an image by use of a printing head capable of ejecting ink.
The present invention is applicable to all appliances using a printing medium, such as paper, cloth, leather, non-woven cloth, OHP sheet, and metal. Specific examples of the appliances include office equipment, such as printers, copiers, and facsimiles, and industrial manufacturing machines.
2. Description of the Related Art
With wide dispersion of copying machines, information processing equipment, such as word-processors and computers, and communication equipment, an inkjet printing apparatus that prints digital images by an inkjet system has rapidly become popular and is often used as an output device in these machines for forming (printing) an image. In these inkjet printing apparatuses, to improve a printing speed, a printing head, in which a plurality of ink ejection nozzles, ink ejection ports, and ink flow channels are densely arranged, is used. Furthermore, with an increase in the requirement for color image formation, a printing apparatus having a plurality of such printing heads has often been seen.
In the inkjet printing system, ink droplets serving as a printing liquid are ejected out of a printing head and landed on a printing medium, such as a paper sheet, to form ink dots to perform printing on the printing medium. Since this printing system is a non-contact printing system in which a printing head is not in contact with a printing medium, noise can be reduced. Furthermore, if nozzles for ejecting ink are densely arranged, a printed image can be formed with a high resolution at a high speed. In addition, a high-quality image can be printed on a printing medium, such as plain paper, at a low cost without requiring any particular treatment, such as development and fixation. In particular, since an on-demand inkjet printing apparatus easily attains color-image formation, and may be miniaturized and simplified, prospective demand is expected in the future. Furthermore, with the tendency toward color image printing, demand to print an image with a high quality at a high speed is increasing.
However, the aforementioned conventional method has various problems as described below.
When a printing head having a plurality of inkjet nozzles integrally and densely arranged therein is used, if one or a plurality of ink ejection nozzles are clogged or fail in function by unknown reasons, ink dots are not formed by the defective nozzle(s) on a printing medium. Such ejection-failure may produce a white streaking on the printed image, deteriorating image quality significantly. On the other hand, a similar problem may occur when ink ejection abnormality takes place from one or a plurality of ejection nozzles, in other words, when ejection-failure of ink takes place for unknown reasons. To be more specific, a printed image with a white streaking or a streaking uneven in density is formed, significantly deteriorating image quality.
The preferred method of improving the quality of a printed image involves an ink ejection state being recovered by a cleaning mechanism when a nozzle causes ejection failure or mal-ejection. Alternatively, use may be made of a multi-pass system in which an image is completely printed by passing (scanning) a printing head a plurality of times. In this method, a nozzle ejecting no ink and a nozzle malfunctioning in ejection (hereinafter referred to as an “ejection-defective, malfunctioning nozzle” or “abnormal nozzle”) are replaced by nozzles complementarily arranged. However, the former method including a recovery operation requires a cleaning time and consumes much ink, increasing cost. In addition, this method is not favorable from an ecological point of view toward reducing ink consumption. In the latter multi-pass method, the printing time is long.
Accordingly, there is a need to develop an inkjet printing apparatus to overcome the aforementioned conventional problems and print an image with a higher quality at a higher speed and lower cost.